Electron discharge device



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' Patented July 28, 1931 UNITED STATES PATENT OFFICE IRVING LANGHUIR, OFSCHENECTADY, NEW YORK, ASSIG NOR 'I'O GENERAL EL ECTBIC COMPANY, ACORPORATION OF NEW- YORK ELECTRON DISCHARGE DEVICE Application filedlarch 10, 1926. Serial No. 93,727.

The present invention relates to the class of electrical dischargedevices which are so constructed that positive ions formed in the spacebetween the electrodes are trapped in a 6 space surrounding the cathodeand by their presence reduce space charge.

Kenneth Kingdom in the Physical Review, Vol. 21, page 408 (1923) and inhis Patent 1,579,117, issued March 30, 1926, has described deviceswhereby the eiiect of gasionization in modifying space charge may beenhanced by preventing the discharge of positiveions. For example, bythe means described, space charge neutralization by positive ions may beobtained in electronic devices in which the gas pressure is so low thatthe gas would otherwise have no appreciable effect on the electricalcharacteristics of the device.

to hereinafter as trapped ion devices.

The present inventlon comprises improvements whereby the efficiency oftrapped ion devices may be increased and whereby such devices arerendered more suitable for control purposes.

Included in my invention is a new form of electric discharge device anda method of op-' eration whereby in part of the space travcrscd byelectrons, ions are trapped with a consequent neutralization of spacecharge, the remainder of the discharge space being traversed by asubstantially pure electron discharge. In this latter part of. the discharge space, the motion of the electrons can '35 be controlled eitherby a magnetic field or by an electric field.

Other novel features of my invention are the following:

' An apparatus and a method whereby the trapped ion effect is increasedor modified by subjecting the current carriers therein to a magneticfield.

An arrangement in a trapped ion device of one or more grids, whereby thecurrent may be modified or controlled without interfering with theaccumulation of positive ions.

An arrangement for securing a joint effect of grids and magnetic fieldfor modifying or controlling the current.

The utilization of the guard members,

Devices of this type will be referred whereby the escape of positiveions is prevented for the control or modification of the current. a a

The above and other features of my invention will be pointed out withgreater particularity in the appended claims and described in detail inthe following specification taken n connection with the accompanyingdrawings.

In the drawings Figs. 1 and 5 illustrate trapped ion devices providedwith means for enhancing gas ionization by a magnetic field; F1gs. 2 and3 illustrate a trapped ion device provided with grid or controlelectrodes;

ig. 4 is a diagram of electrical connections,

suitable for use with the apparatus shown in Figs. .2 and 3; Figs. 5 and6 illustrate diagrammatically a device in which the combmed effect of agrid and a magnetic winding is obtained; and Fig 7 is a cross section ofa modified form of anode.

The device shown in Fig. 1 comprises an evacuated envelope 1 containinga filamentary cathode 2, and a cylindrical anode 3 which preferably isarranged symmetrically about the cathode. The cathode may consist oftungsten, tantalum, or other material which, when heated, willeffectively emit electrons. It is supported by the sealed-in conductors4, 5; a spring 6 preferably being inserted to maintain the cathode taut.The anode 3 may consist of nickel, molybdenum or the like and may beheld frictionally in a desired position by coiled springs 7, 8.sealed-in anode conductor 9 is provided as usual.. The end plates orguards 10, 11 are supported by the wires 12, 13 and 14, 15 respectively,the wires 13 and 15 being conducted through nal contact devices (notshown). They may be positively charged as by being connected to theanode or to the external source of positive potential to prevent theescape of positive ions.

The residual gas pressure within the container 1 should be so low thatin the absence of trapped ions, a substantially pure electron dischargecan take place between the electhe stems 16, 17 to suitable exterofpositive ions is negligibly low.

This much of the device of Fig. 1 does not differ essentially from thetrapped ion device described in the above Kingdon patent. I havediscovered, however, that contrary to what might be expected by reasonof the enormously greater'elfect of a magnetic field upon the mbtion ofelectrons as compared with the eifect of a magnetic field upon positiveions, the trapping of ions may enhanced by a magnetic field which isinsufiicient to cut off the electron current by the method described byA. W. Hull in United States Patent 1,523,776 and in the Journal of theAmerican Institute of Electrical Engineers for September, 1921, page715.

An external magnetizing winding 18 is provided about the trapped iondevice for generating a magnetic field, a component of which is parallelto the cathode and which imparts to both the electrons and the ionsmotion in a tangential direction, that is, gives them an angularvelocity about the cathode. As a consequence the orbits ofboth the electrons and the ions are curved. The amount 7 of curvature of the orbitsdepends on various factors, such as the mass of the electrons or ions,the propelling voltage and the magnetic field strength. The deflectingforce in the case of an ion moving from a point near the anode 3 to thefilamentary cathode 2 need only be small to cause an ion to miss thefilamentary cathode and to execute orbits to and fro about it for anappreciable interval.

The angular momentum of an ion is equal to the product of the mass, thetangential velocity and the radius. It remains constant (assuming asymmetrical device) even though the ion moves toward the cathode. Henceas the radius decreases, the mass being constant, the tangentialvelocity increases. In the case of the electrons moving from the cathodeto the anode the tangential velocity decreases. A magnetic field lessthan the cut oil value, that is, a field giving the electrons a radiusof curvature which is greater than half the radius of curvature of theanode approximately) permits the electrons to reach the anode eventhough their path is curved by the magnetic field. In other words, inthe case of the positive ions, with a chosen gas and a propercorrelation of conditions, in particular the voltages on the tube, andthe ratios of cathode and anode diameters, this magnification of thetangential velocity permits an applied magnetic field, which is belowthe value at which the flow of electrons from cathode to anode becomesreduced or prevented by the action of the magnetic field, to enhance thetrapping of the positive ions.

By an increase of magnetic field within a working range the accumulationof positive ions increases with a given gas pressure and converselywit-h a decrease ofmagnetic field the positive ion accumulationdecreases. As the current carrying capacity of a-trapped ion devicevaries with the number of ions trapped, the electron current between theelectrodes 2, 3 may be varied by varying the magnetic field withinworking limits.

In the absence of a magnetic field the ratio of anode diameter tocathode diameter preferably should be about 200 to 1 or greater.

en using a magnetic field an efiective trapping of ions maybe obtainedwith smaller ratios and hence heavier or larger diameter. cathodeconductors can be utilized without the sacrifice ofefliciency. Theefiect of a magnetic field is most marked in the case of light gases,such as hydrogen or helium. The gaspressure ordinarily should be lessthan about a micron of mercury pressure but will vary with the kind ofgas used.

As shown in Fig. 5, a magnetic field may be used to advantage incombination with a grid in a trapped ion device. In the device" hereillustrated a grid: 20 is interposed between the cathode 2 and the anode3' As shown in Figs. 5 and 6 the grid 20, consisting of longitudinalwires, is supported between the rings 21, 21. 'When the grid 20 and theguard plates 22, 23 are positively charged to a sufliciently highpotential, materially above the ionizing potential of the gas in thetube, say to fifty volts or higher, the positive ions are trapped withinthe space enclosed by the grid and guard plates and neutralize electronspace charge.

Most of the electrons pass through the spaces between the members of thegrid 20 and flow to the positively charged anode 3. The grid 20 may besaid to act as a virtual cathode because it is the effective source ofthe electrons which are controlled by the magnetic field generated bythe winding 24. Between the grid 20 and the anode 3, the conditions of asubstantially pure electron discharge exist, and the electrons arecontrolled by the magnetic field, as in the magnetron,

which is described in United States patent to rent for the cathode 2 anda space current through the device by being connected to the anode 3 bya conductor 33. The outer grid 26' is connected to a circuit 34, theopposite terminal of which is connected to the cathode circuit 32,preferably in series, with a polarizing battery 35. An input circuit 36is connected to the primary of a transformer 37, the secondary of whichis intercalated in the vaned.

v by the positive and a lower or a circuit 34 to impress suitablepotential variations on the grid 26. The conductors 38, 39, leading toguard plates 27, 28 may be con nected by the conductor'40 either to anintermediate positive terminal-of the battery through the conductor 29or may be connected directly to the anode, 3 by a conductor 42. A switch43 is provided whereby either connection may be made or the end platesmay be disconnected from either circuit.

In the space between the grid 25 and the anode 3 the conditions of pureelectron conduction are present. 7 The electron current may becontrolled in the usual manner by the grid 26 which ay receive fromthe'in'put circuit-'34 potential variationsv of audio or radiofrequency. 5

Includedin the inner grid circuit 29, 29' is the secondary of atransformer-44' (preferably an audio frequency transformer) whereon thegrid 25 and t e guards 27,28 may be variedthereby ,con-

b the positive potential trolling the amount of positive ionization inthe device- In other words, by means of an input device which issymbolically represented by the transformer 44 the current carryingcapacity of the device may When the grid 25 is charged to a'sufiiciently high positive potential in excess of the ionizingpotential of the residual gas, it is effective m cooperating witlr theend plates to trap the ions in the space enclosed by the grid 25 butwhen its potential becomes less positive or becomes negative, then thegrid 25 becomes ineffective. This 'may occur at audio freriiency in aradio sendineguapparatus and ma used to vary the lou ess of the signalsing transmitted by the output circuit'45 which is coupled to the platecircuit 33 by a high frequency transformer 46.

In some cases, one of thegrids, for example, the grid 26, may be omittedand the current may be controlled or modified entirely ment is mostefiective when the potential of thegrid 25 swings between a positivevalue approximating the potential of the anode negative value, as in anoscillator. A

Fig. 7 is an en 47 t at is, an anode having longitudinally extendingconvolutions whereby the deflection of the ions cathode is enhanced.

In the case of Figs. 2, 3, 5, 6 and 7 the outer envelope of the devicehas been omitted in the drawings but its presence in the physical--devices is assumed.

- What I claim as new and desireto secure by Letters Patent of theUnited States, is:- 1. The combination of means for generating anelectron-discharge accompamed by an amount of positive ionization whichis insuflicient to materially neutralize space cathode,

.means for imparting to closure, means located grid 25. Such an arrange-.hand this 9th day of March, 1926.-

from a direct. path to the char e, means for traplping positive ions inthe ischarge space an magnetic means for varying the e ectiveness ofsaid trapping means.

2. The. combination "of a linear thermionic an anode surrounding thesame, an evacuated enclosure for said electrodes, means for trappingpositive ions in a space surrounding said cathode. and magnetic ions insaid space I an angular momentum about said cathode whereby theefiectiveness of the trapping means is increased.

3. The combination of a linear thermionic cathode, a cylindrical anodesymmetrically spaced about said cathode, an evacuated enat the ends ofsaid anode for trapping ions in the discharge space therein, a gridsurrounding said cathode and spaced away from said anode, a grid adaptedto be charged sufliciently positive to enhance the effect of said iontrapping means, and means for generating a magnetic field in said devicehaving a component at right angles to the orbits of electrons passingfrom cathode to anode still further-to enhance the ion trappingfunction. 1

4. The'method discharge in an attenuated gas which con' slsts inimpressing upon said discharge a magnetic field having a component atright angles to said discharge and having a strength charge but beingcapable of materially increasing the production of positive ions by saiddischarge and trapping positive ionsin the discharge space. Y

5. The method of operatingan electron discharge in an attenuated gaswhich consists in trapping positive'ions adjacent the cathode,subjecting said discharge to a magnetic field applied at right anglesthereto, and varying said trapped ion space.

In witness whereof, I have hereto set my IRVING LANGMUI-R.

view of a corrugated anode of operating an electron insuflicient tosuppress said dis discharge external to the

